What's the nicest London restaurant to which you would take a six-year-old?

My family will be in London for Thanksgiving week this year. Though we're not trying to find a turkey dinner, we would like to go somewhere special on Thanksgiving. If it were just my husband and me, we would choose the Fat Duck, Ledbury, or The Square (all based on this board's recommendations.) However, we will have our six-year-old son with us, and we'll have spent a day doing touristic things, so he'll probably be tired and possibly not capable of his best behavior.

He is a great kid and we've taken him to Taillevent, Il Convivio, Gramercy Tavern, Eleven Madison Park, La Degustation Boheme in Prague, and many other wonderful places, and he's never let us down. But we are careful to eat early (doesn't seem to be an option with these London restaurants) and the places I've mentioned (at least the last three) are kind of noisy anyway, so any crabbiness on his part goes unnoticed by those at nearby tables.

So what recommendations do you have? What is the nicest place you would take a kid? Don't worry about the menu; he's a good eater and will try most things, and worst case scenario is he gets a pricey chicken breast or plate of pasta. But we don't want to feel like other diners are giving us the stink eye, or be somewhere very quiet where everyone can hear him begging fruitlessly for his Nintendo DS. It will be our Thanksgiving dinner, so we want to treat ourselves to something nice, but want to be respectful of the other people around us.